The ultraviolet spectrum generally is divided into three regions: UVA (400 nm-320 nm), UVB (320 nm-290 nm) and UVC (290 nm-200 nm). The UVA and UVB regions are important for suntan lamps and medical phototherapy applications and the UVC is important for germicidal lamp applications. The phosphors used in these applications are typically intended for stimulation with the type of low pressure mercury discharge used in conventional fluorescent lamps which generates primarily 254 nm radiation.
U.S. Pat. No. 4,757,233 describes a ultraviolet (UV)-emitting cerium-activated calcium pyrophosphate phosphor. The phosphor formulation is given as Ca(2−w−x−y)(NSF)wCexNayP2O7, where NSF is the nonstoichiometric factor, and w ranges from 0 to 0.1, x ranges from 0.05 to 0.20, and y ranges from 0.05 to 0.20. The nonstoichiometric factor is an idea common to many phosphors where a small excess of anionic species is used in the formulated phosphor blend and results in improved brightness for the fired phosphor material. The amount of Na+ in the phosphor formulation is approximately equal to the amount of Ce3+ in the phosphor for overall charge balance. The Ce-activated calcium pyrophosphate phosphor is stimulated by 254 nm radiation and has an emission peak in the UVB region at about 330 nm.